Method and apparatus for configuring qcl between antenna ports for massive mimo in a wireless communication system

ABSTRACT

A method for receiving a Reference Signal (RS) at a User Equipment (UE) in a wireless communication system is disclosed. The method includes receiving information about a plurality of RSs through a high layer, and receiving the RS based on the information about the plurality of RSs from at least one node. The information about the plurality of RSs includes information indicating whether it is possible to assume quasi co-location between at least two RSs of the plurality of RSs.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for configuring QuasiCo-Location (QCL) between antenna ports for massive Multiple InputMultiple Output (MIMO) (i.e. MIMO with a large number of antennas) in awireless communication system.

BACKGROUND ART

A brief description will be given of a 3rd Generation PartnershipProject Long Term Evolution (3GPP LTE) system as an example of awireless communication system to which the present invention can beapplied.

FIG. 1 illustrates a configuration of an Evolved Universal MobileTelecommunications System (E-UMTS) network as an exemplary wirelesscommunication system. The E-UMTS system is an evolution of the legacyUMTS system and the 3GPP is working on the basics of E-UMTSstandardization. E-UMTS is also called an LTE system. For details of thetechnical specifications of UMTS and E-UMTS, refer to Release 7 andRelease 8 of “3rd Generation Partnership Project; TechnicalSpecification Group Radio Access Network”, respectively.

Referring to FIG. 1, the E-UMTS system includes a User Equipment (UE),an evolved Node B (eNode B or eNB), and an Access Gateway (AG) which islocated at an end of an Evolved UMTS Terrestrial Radio Access Network(E-UTRAN) and connected to an external network. The eNB may transmitmultiple data streams simultaneously, for broadcast service, multicastservice, and/or unicast service.

A single eNB manages one or more cells. A cell is set to operate in oneof the bandwidths of 1.25, 2.5, 5, 10, 15 and 20 Mhz and providesDownlink (DL) or Uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be configured so as to providedifferent bandwidths. An eNB controls data transmission and reception toand from a plurality of UEs. Regarding DL data, the eNB notifies aparticular UE of a time-frequency area in which the DL data is supposedto be transmitted, a coding scheme, a data size, Hybrid Automatic RepeatreQuest (HARD) information, etc. by transmitting DL schedulinginformation to the UE. Regarding UL data, the eNB notifies a particularUE of a time-frequency area in which the UE can transmit data, a codingscheme, a data size, HARQ information, etc. by transmitting ULscheduling information to the UE. An interface for transmitting usertraffic or control traffic may be defined between eNBs. A Core Network(CN) may include an AG and a network node for user registration of UEs.The AG manages the mobility of UEs on a Tracking Area (TA) basis. A TAincludes a plurality of cells.

While the development stage of wireless communication technology hasreached LTE based on Wideband Code Division Multiple Access (WCDMA), thedemands and expectation of users and service providers are increasing.Considering that other radio access technologies are under development,a new technological evolution is required to achieve futurecompetitiveness. Specifically, cost reduction per bit, increased serviceavailability, flexible use of frequency bands, a simplified structure,an open interface, appropriate power consumption of UEs, etc. arerequired.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ona method and apparatus for configuring Quasi Co-Location (QCL) betweenantenna ports to implement massive Multiple Input Multiple Output (MIMO)in a wireless communication system.

Technical Solution

The object of the present invention can be achieved by providing amethod for receiving a Reference Signal (RS) at a User Equipment (UE) ina wireless communication system, including receiving information about aplurality of RSs through a high layer, and receiving the RS based on theinformation about the plurality of RSs from at least one node. Theinformation about the plurality of RSs includes information indicatingwhether it is possible to assume quasi co-location between at least twoRSs of the plurality of RSs.

In another aspect of the present invention, provided herein is a methodfor transmitting an RS to a UE by a network in a wireless communicationsystem, including transmitting information about a plurality of RSs tothe UE through a high layer, and transmitting the RS based on theinformation about the plurality of RSs to the UE through at least onenode. The information about the plurality of RSs includes informationindicating whether it is possible to assume quasi co-location between atleast two RSs of the plurality of RSs.

If it is possible to assume quasi co-location between at least two RSsof the plurality of RSs, the UE may assume that the at least two RSshave a same large-scale property. The large-scale property may includeat least one of Doppler spread, Doppler shift, average delay, and delayspread.

The RS may be a Channel State Information Reference Signal (CSI-RS).

The at least two RSs assumed to be quasi co-located may be transmittedthrough the same node.

One of the at least two RSs may be a default RS, and the informationindicating whether it is possible to assume quasi co-location betweenthe at least two RSs of the plurality of RSs may include informationindicating whether it is possible to assume that another RS of the atleast two RSs is quasi co-located with the default RS.

The information about the plurality of RSs may include resourceconfiguration information about each of the plurality of RSs, theresource configuration information having a specific field for quasico-location assumption, and if the specific fields of the resourceconfiguration information about at least two RSs are same, it may bepossible for the UE to assume that the at least two RSs are quasico-located.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved with the present invention are not limited to whathas been particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

Advantageous Effects

According to embodiments of the present invention, QCL can beefficiently configured between antenna ports for massive MIMO in awireless communication system.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 illustrates a configuration of an Evolved Universal MobileTelecommunications System (E-UMTS) network as an example of a wirelesscommunication system;

FIG. 2 illustrates a control-plane protocol stack and a user-planeprotocol stack in a radio interface protocol architecture conforming toa 3rd Generation Partnership Project (3GPP) radio access networkstandard between a User Equipment (UE) and an Evolved UMTS TerrestrialRadio Access Network (E-UTRAN);

FIG. 3 illustrates physical channels and a general signal transmissionmethod using the physical channels in a 3GPP system;

FIG. 4 illustrates a structure of a radio frame in a Long Term Evolution(LTE) system;

FIG. 5 illustrates a structure of a downlink radio frame in the LTEsystem;

FIG. 6 illustrates a structure of an uplink subframe in the LTE system;

FIG. 7 illustrates a configuration of a general Multiple Input MultipleOutput (MIMO) communication system;

FIGS. 8 and 9 illustrate downlink Reference Signal (RS) configurationsin an LTE system supporting downlink transmission through four antennas(4-Tx downlink transmission);

FIG. 10 illustrates an exemplary downlink Demodulation Reference Signal(DMRS) allocation defined in a current 3GPP standard specification;

FIG. 11 illustrates Channel State Information-Reference Signal (CSI-RS)configuration #0 of downlink CSI-RS configurations defined in a current3GPP standard specification;

FIG. 12 illustrates antenna tilting schemes;

FIG. 13 is a view comparing an antenna system of the related art with anActive Antenna System (AAS);

FIG. 14 illustrates an exemplary AAS-based User Equipment (UE)-specificbeamforming;

FIG. 15 illustrates an AAS-based two-dimensional beam transmissionscenario;

FIG. 16 illustrates an exemplary allocation of multiple Channel StateInformation Reference Signal (CSI-RS) resources to a single UE accordingto an embodiment of the present invention; and

FIG. 17 is a block diagram of a communication apparatus according to anembodiment of the present invention.

BEST MODE

The configuration, operation, and other features of the presentinvention will readily be understood with embodiments of the presentinvention described with reference to the attached drawings. Embodimentsof the present invention as set forth herein are examples in which thetechnical features of the present invention are applied to a 3rdGeneration Partnership Project (3GPP) system.

While embodiments of the present invention are described in the contextof Long Term Evolution (LTE) and LTE-Advanced (LTE-A) systems, they arepurely exemplary. Therefore, the embodiments of the present inventionare applicable to any other communication system as long as the abovedefinitions are valid for the communication system. In addition, whilethe embodiments of the present invention are described in the context ofFrequency Division Duplexing (FDD), they are also readily applicable toHalf-FDD (H-FDD) or Time Division Duplexing (TDD) with somemodifications.

The term ‘Base Station (BS)’ may be used to cover the meanings of termsincluding Remote Radio Head (RRH), evolved Node B (eNB or eNode B),Reception Point (RP), relay, etc.

FIG. 2 illustrates control-plane and user-plane protocol stacks in aradio interface protocol architecture conforming to a 3GPP wirelessaccess network standard between a User Equipment (UE) and an EvolvedUMTS Terrestrial Radio Access Network (E-UTRAN). The control plane is apath in which the UE and the E-UTRAN transmit control messages to managecalls, and the user plane is a path in which data generated from anapplication layer, for example, voice data or Internet packet data istransmitted.

A PHYsical (PHY) layer at Layer 1 (L1) provides information transferservice to its higher layer, a Medium Access Control (MAC) layer. ThePHY layer is connected to the MAC layer via transport channels. Thetransport channels deliver data between the MAC layer and the PHY layer.Data is transmitted on physical channels between the PHY layers of atransmitter and a receiver. The physical channels use time and frequencyas radio resources. Specifically, the physical channels are modulated inOrthogonal Frequency Division Multiple Access (OFDMA) for Downlink (DL)and in Single Carrier Frequency Division Multiple Access (SC-FDMA) forUplink (UL).

The MAC layer at Layer 2 (L2) provides service to its higher layer, aRadio Link Control (RLC) layer via logical channels. The RLC layer at L2supports reliable data transmission. RLC functionality may beimplemented in a function block of the MAC layer. A Packet DataConvergence Protocol (PDCP) layer at L2 performs header compression toreduce the amount of unnecessary control information and thusefficiently transmit Internet Protocol (IP) packets such as IP version 4(IPv4) or IP version 6 (IPv6) packets via an air interface having anarrow bandwidth.

A Radio Resource Control (RRC) layer at the lowest part of Layer 3 (orL3) is defined only on the control plane. The RRC layer controls logicalchannels, transport channels, and physical channels in relation toconfiguration, reconfiguration, and release of radio bearers. A radiobearer refers to a service provided at L2, for data transmission betweenthe UE and the E-UTRAN. For this purpose, the RRC layers of the UE andthe E-UTRAN exchange RRC messages with each other. If an RRC connectionis established between the UE and the E-UTRAN, the UE is in RRCConnected mode and otherwise, the UE is in RRC Idle mode. A Non-AccessStratum (NAS) layer above the RRC layer performs functions includingsession management and mobility management.

DL transport channels used to deliver data from the E-UTRAN to UEsinclude a Broadcast Channel (BCH) carrying system information, a PagingChannel (PCH) carrying a paging message, and a Shared Channel (SCH)carrying user traffic or a control message. DL multicast traffic orcontrol messages or DL broadcast traffic or control messages may betransmitted on a DL SCH or a separately defined DL Multicast Channel(MCH). UL transport channels used to deliver data from a UE to theE-UTRAN include a Random Access Channel (RACH) carrying an initialcontrol message and a UL SCH carrying user traffic or a control message.Logical channels that are defined above transport channels and mapped tothe transport channels include a Broadcast Control Channel (BCCH), aPaging Control Channel (PCCH), a Common Control Channel (CCCH), aMulticast Control Channel (MCCH), a Multicast Traffic Channel (MTCH),etc.

FIG. 3 illustrates physical channels and a general method fortransmitting signals on the physical channels in the 3GPP system.

Referring to FIG. 3, when a UE is powered on or enters a new cell, theUE performs initial cell search (S301). The initial cell search involvesacquisition of synchronization to an eNB. Specifically, the UEsynchronizes its timing to the eNB and acquires a cell Identifier (ID)and other information by receiving a Primary Synchronization Channel(P-SCH) and a Secondary Synchronization Channel (S-SCH) from the eNB.Then the UE may acquire information broadcast in the cell by receiving aPhysical Broadcast Channel (PBCH) from the eNB. During the initial cellsearch, the UE may monitor a DL channel state by receiving a DownLinkReference Signal (DL RS).

After the initial cell search, the UE may acquire detailed systeminformation by receiving a Physical Downlink Control Channel (PDCCH) andreceiving a Physical Downlink Shared Channel (PDSCH) based oninformation included in the PDCCH (S302).

If the UE initially accesses the eNB or has no radio resources forsignal transmission to the eNB, the UE may perform a random accessprocedure with the eNB (S303 to S306). In the random access procedure,the UE may transmit a predetermined sequence as a preamble on a PhysicalRandom Access Channel (PRACH) (S303 and S305) and may receive a responsemessage to the preamble on a PDCCH and a PDSCH associated with the PDCCH(S304 and S306). In the case of a contention-based RACH, the UE mayadditionally perform a contention resolution procedure.

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S307) and transmit a Physical Uplink Shared Channel(PUSCH) and/or a Physical Uplink Control Channel (PUCCH) to the eNB(S308), which is a general DL and UL signal transmission procedure.Particularly, the UE receives Downlink Control Information (DCI) on aPDCCH. Herein, the DCI includes control information such as resourceallocation information for the UE. Different DCI formats are definedaccording to different usages of DCI.

Control information that the UE transmits to the eNB on the UL orreceives from the eNB on the DL includes a DL/UL ACKnowledgment/NegativeACKnowledgment (ACK/NACK) signal, a Channel Quality Indicator (CQI), aPrecoding Matrix Index (PMI), a Rank Indicator (RI), etc. In the 3GPPLTE system, the UE may transmit control information such as a CQI, aPMI, an RI, etc. on a PUSCH and/or a PUCCH.

FIG. 4 illustrates a structure of a radio frame used in the LTE system.

Referring to FIG. 4, a radio frame is 10 ms (327200×T_(s)) long anddivided into 10 equal-sized subframes. Each subframe is 1 ms long andfurther divided into two slots. Each time slot is 0.5 ms (15360×T_(s))long. Herein, T_(s) represents a sampling time and T_(s)=1/(15kHz×2048)=3.2552×10⁻⁸ (about 33 ns). A slot includes a plurality ofOrthogonal Frequency Division Multiplexing (OFDM) symbols or SC-FDMAsymbols in the time domain by a plurality of Resource Blocks (RBs) inthe frequency domain. In the LTE system, one RB includes 12 subcarriersby 7 (or 6) OFDM symbols. A unit time during which data is transmittedis defined as a Transmission Time Interval (TTI). The TTI may be definedin units of one or more subframes. The above-described radio framestructure is purely exemplary and thus the number of subframes in aradio frame, the number of slots in a subframe, or the number of OFDMsymbols in a slot may vary.

FIG. 5 illustrates exemplary control channels included in a controlregion of a subframe in a DL radio frame.

Referring to FIG. 5, a subframe includes 14 OFDM symbols. The first oneto three OFDM symbols of a subframe are used for a control region andthe other 13 to 11 OFDM symbols are used for a data region according toa subframe configuration. In FIG. 5, reference characters R1 to R4denote RSs or pilot signals for antenna 0 to antenna 3. RSs areallocated in a predetermined pattern in a subframe irrespective of thecontrol region and the data region. A control channel is allocated tonon-RS resources in the control region and a traffic channel is alsoallocated to non-RS resources in the data region. Control channelsallocated to the control region include a Physical Control FormatIndicator Channel (PCFICH), a Physical Hybrid-ARQ Indicator Channel(PHICH), a Physical Downlink Control Channel (PDCCH), etc.

The PCFICH is a physical control format indicator channel carryinginformation about the number of OFDM symbols used for PDCCHs in eachsubframe. The PCFICH is located in the first OFDM symbol of a subframeand configured with priority over the PHICH and the PDCCH. The PCFICHincludes 4 Resource Element Groups (REGs), each REG being distributed tothe control region based on a cell Identity (ID). One REG includes 4Resource Elements (REs). An RE is a minimum physical resource defined byone subcarrier by one OFDM symbol. The PCFICH is set to 1 to 3 or 2 to 4according to a bandwidth. The PCFICH is modulated in Quadrature PhaseShift Keying (QPSK).

The PHICH is a physical Hybrid-Automatic Repeat and request (HARQ)indicator channel carrying an HARQ ACK/NACK for a UL transmission. Thatis, the PHICH is a channel that delivers DL ACK/NACK information for ULHARQ. The PHICH includes one REG and is scrambled cell-specifically. AnACK/NACK is indicated in one bit and modulated in Binary Phase ShiftKeying (BPSK). The modulated ACK/NACK is spread with a Spreading Factor(SF) of 2 or 4. A plurality of PHICHs mapped to the same resources forma PHICH group. The number of PHICHs multiplexed into a PHICH group isdetermined according to the number of spreading codes. A PHICH (group)is repeated three times to obtain a diversity gain in the frequencydomain and/or the time domain.

The PDCCH is a physical DL control channel allocated to the first n OFDMsymbols of a subframe. Herein, n is 1 or a larger integer indicated bythe PCFICH. The PDCCH occupies one or more CCEs. The PDCCH carriesresource allocation information about transport channels, PCH andDL-SCH, a UL scheduling grant, and HARQ information to each UE or UEgroup. The PCH and the DL-SCH are transmitted on a PDSCH. Therefore, aneNB and a UE transmit and receive data usually on the PDSCH, except forspecific control information or specific service data.

Information indicating one or more UEs to receive PDSCH data andinformation indicating how the UEs are supposed to receive and decodethe PDSCH data are delivered on a PDCCH. For example, on the assumptionthat the Cyclic Redundancy Check (CRC) of a specific PDCCH is masked byRadio Network Temporary Identity (RNTI) “A” and information about datatransmitted in radio resources (e.g. at a frequency position) “B” basedon transport format information (e.g. a transport block size, amodulation scheme, coding information, etc.) “C” is transmitted in aspecific subframe, a UE within a cell monitors, that is, blind-decodes aPDCCH using its RNTI information in a search space. If one or more UEshave RNTI “A”, these UEs receive the PDCCH and receive a PDSCH indicatedby “B” and “C” based on information of the received PDCCH.

FIG. 6 illustrates a structure of a UL subframe in the LTE system.

Referring to FIG. 6, a UL subframe may be divided into a control regionand a data region. A Physical Uplink Control Channel (PUCCH) includingUplink Control Information (UCI) is allocated to the control region anda Physical uplink Shared Channel (PUSCH) including user data isallocated to the data region. The middle of the subframe is allocated tothe PUSCH, while both sides of the data region in the frequency domainare allocated to the PUCCH. Control information transmitted on the PUCCHmay include an HARQ ACKINACK, a CQI representing a downlink channelstate, an RI for Multiple Input Multiple Output (MIMO), a SchedulingRequest (SR) requesting UL resource allocation. A PUCCH for one UEoccupies one RB in each slot of a subframe. That is, the two RBsallocated to the PUCCH are frequency-hopped over the slot boundary ofthe subframe. Particularly, PUCCHs with m=0, m=1, and m=2 are allocatedto a subframe in FIG. 6.

Now a description will be given of a MIMO system. MIMO can increase thetransmission and reception efficiency of data by using a plurality ofTransmission (Tx) antennas and a plurality of Reception (Rx) antennas.That is, with the use of multiple antennas at a transmitter or areceiver, MIMO can increase capacity and improve performance in awireless communication system. The term “MIMO” is interchangeable with‘multi-antenna’.

The MIMO technology does not depend on a single antenna path to receivea whole message. Rather, it completes the message by combining datafragments received through a plurality of antennas. MIMO can increasedata rate within a cell area of a predetermined size or extend systemcoverage at a given data rate. In addition, MIMO can find its use in awide range including mobile terminals, relays, etc. MIMO can overcome alimited transmission capacity encountered with the conventionalsingle-antenna technology in mobile communication.

FIG. 7 illustrates the configuration of a typical MIMO communicationsystem. Referring to FIG. 7, a transmitter has N_(T) Tx antennas and areceiver has N_(R) Rx antennas. The use of a plurality of antennas atboth the transmitter and the receiver increases a theoretical channeltransmission capacity, compared to the use of a plurality of antennas atonly one of the transmitter and the receiver. The channel transmissioncapacity increases in proportion to the number of antennas. Therefore,transmission rate and frequency efficiency are increased. Given amaximum transmission rate R_(o) that may be achieved with a singleantenna, the transmission rate may be increased, in theory, to theproduct of R_(o) and a transmission rate increase rate R_(i) in the caseof multiple antennas. R_(i) is the smaller value between N_(T) andN_(R).

R _(i)=min(N _(T) ,N _(R))   [Equation 1]

For instance, a MIMO communication system with four Tx antennas and fourRx antennas may achieve a four-fold increase in transmission ratetheoretically, relative to a single-antenna system. Since thetheoretical capacity increase of the MIMO system was verified in themiddle 1990s, many techniques have been actively proposed to increasedata rate in real implementation. Some of the techniques have alreadybeen reflected in various wireless communication standards such asstandards for 3G mobile communications, future-generation Wireless LocalArea Network (WLAN), etc.

Concerning the research trend of MIMO up to now, active studies areunderway in many aspects of MIMO, inclusive of studies of informationtheory related to calculation of multi-antenna communication capacity indiverse channel environments and multiple access environments, studiesof measuring MIMO radio channels and MIMO modeling, studies oftime-space signal processing techniques to increase transmissionreliability and transmission rate, etc.

Communication in a MIMO system with N_(T) Tx antennas and N_(R) Rxantennas as illustrated in FIG. 7 will be described in detail throughmathematical modeling. Regarding a transmission signal, up to N_(T)pieces of information can be transmitted through the N_(T) Tx antennas,as expressed as the following vector.

s=[s₁,s₂, . . . , s_(N) _(T) ]^(T)   [Equation 2]

A different transmission power may be applied to each piece oftransmission information, s₁,s₂, . . . , s_(N) _(T) . Let thetransmission power levels of the transmission information be denoted byP₁,P₂, . . . , P_(N) _(T) , respectively. Then the transmissionpower-controlled transmission infoimation vector is given as

ŝ=[ŝ₁,ŝ₂, . . . , ŝ_(N) _(T) ]^(T)=[P₁s₁,P₂s₂, . . . , P_(N) _(T) s_(N)_(T) ]^(T)   [Equation 3]

The transmission power-controlled transmission information vector ŝ maybe expressed as follows, using a diagonal matrix P of transmissionpower.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

N_(T) transmission signals x₁,x₂, . . . , x_(N) _(T) may be generated bymultiplying the transmission power-controlled information vector ŝ by aweight matrix W. The weight matrix W functions to appropriatelydistribute the transmission information to the Tx antennas according totransmission channel states, etc. These N_(T) transmission signalsx₁,x₂, . . . , x_(N) _(T) are represented as a vector X, which may bedetermined by [Equation 5]. Herein, w_(ij) denotes a weight between aj^(th) piece of information and an i^(th) Tx antenna and W is referredto as a weight matrix or a precoding matrix.

$\begin{matrix}{x = {\left\lbrack \begin{matrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{matrix} \right\rbrack = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1\; N_{T}} \\w_{21} & w_{22} & \ldots & w_{2\; N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In general, the rank of a channel matrix is the maximum number ofdifferent pieces of information that can be transmitted on a givenchannel, in its physical meaning. Therefore, the rank of a channelmatrix is defined as the smaller between the number of independent rowsand the number of independent columns in the channel matrix. The rank ofthe channel matrix is not larger than the number of rows or columns ofthe channel matrix. The rank of a channel matrix H, rank(H) satisfiesthe following constraint.

rank(H)≦min(N _(T) ,N _(R))   [Equation 6]

A different piece of information transmitted in MIMO is referred to as‘transmission stream’ or shortly ‘stream’. The ‘stream’ may also becalled ‘layer’. It is thus concluded that the number of transmissionstreams is not larger than the rank of channels, i.e. the maximum numberof different pieces of transmittable information. Thus, the channelmatrix H is determined by

# of streams≦rank(H)≦min(N _(T) ,N _(R))   [Equation 7]

“# of streams” denotes the number of streams. One thing to be notedherein is that one stream may be transmitted through one or moreantennas.

One or more streams may be mapped to a plurality of antennas in manyways. The stream-to-antenna mapping may be described as followsdepending on MIMO schemes. If one stream is transmitted through aplurality of antennas, this may be regarded as spatial diversity. When aplurality of streams are transmitted through a plurality of antennas,this may be spatial multiplexing. Needless to say, a hybrid scheme ofspatial diversity and spatial multiplexing in combination may becontemplated.

It is expected that the future-generation mobile communication standard,LTE-A will support Coordinated Multi-Point (CoMP) transmission in orderto increase data rate, compared to the legacy LTE standard. CoMP refersto transmission of data to a UE through cooperation from two or moreeNBs or cells in order to increase communication performance between aUE located in a shadowing area and an eNB (a cell or sector).

CoMP transmission schemes may be classified into CoMP-Joint Processing(CoMP-JP) called cooperative MIMO characterized by data sharing, andCoMP-Coordinated Scheduling/Beamforming (CoMP-CS/CB).

In DL CoMP-JP, a UE may instantaneously receive data simultaneously fromeNBs that perform CoMP transmission and may combine the receivedsignals, thereby increasing reception performance (Joint Transmission(JT)). In addition, one of the eNBs participating in the CoMPtransmission may transmit data to the UE at a specific time point(Dynamic Point Selection (DPS)).

In contrast, in downlink CoMP-CS/CB, a UE may receive datainstantaneously from one eNB, that is, a serving eNB by beamforming.

In UL CoMP-JP, eNBs may receive a PUSCH signal from a UE at the sametime (Joint Reception (JR)). In contrast, in UL CoMP-CS/CB, only one eNBreceives a PUSCH from a UE. Herein, cooperative cells (or eNBs) may makea decision as to whether to use CoMP-CS/CB.

Now a detailed description will be given of RS.

In general, a transmitter transmits an RS known to both the transmitterand a receiver along with data to the receiver so that the receiver mayperform channel measurement in the RS. The RS indicates a modulationscheme for demodulation as well as the RS is used for channelmeasurement. The RS is classified into Dedicated RS (DRS) for a specificUE (i.e. UE-specific RS) and Common RS (CRS) for all UEs within a cell(i.e. cell-specific RS). The cell-specific RS includes an RS in which aUE measures a CQI/PMI/RI to be reported to an eNB. This RS is referredto as Channel State Information-RS (CSI-RS).

FIGS. 8 and 9 illustrate RS configurations in an LTE system supportingDL transmission through four antennas (4-Tx DL transmission).Specifically, FIG. 8 illustrates an RS configuration in the case of anormal CP and FIG. 9 illustrates an RS configuration in the case of anextended CP.

Referring to FIGS. 8 and 9, reference numerals 0 to 3 in grids denotecell-specific RSs, CRSs transmitted through antenna port 0 to antennaport 3, for channel measurement and data modulation. The CRSs may betransmitted to UEs across a control information region as well as a datainformation region.

Reference character D in grids denotes UE-specific RSs, Demodulation RSs(DMRSs). The DMRSs are transmitted in a data region, that is, on aPDSCH, supporting single-antenna port transmission. The existence orabsence of a UE-specific RS, DMRS is indicated to a UE by higher-layersignaling. In FIGS. 8 and 9, the DMRSs are transmitted through antennaport 5. 3GPP TS 36.211 defines DMRSs for a total of eight antenna ports,antenna port 7 to antenna port 14.

FIG. 10 illustrates an exemplary DL DMRS allocation defined in a current3GPP standard specification.

Referring to FIG. 10, DMRSs for antenna ports 7, 8, 11, and 13 aremapped using sequences for the respective antenna ports in a first DMRSgroup (DMRS Group 1), whereas DMRSs for antenna ports 9, 10, 12, and 14are mapped using sequences for the respective antenna ports in a secondDMRS group (DMRS Group 2).

As compared to CRS, CSI-RS was proposed for channel measurement of aPDSCH and up to 32 different resource configurations are available forCSI-RS to reduce Inter-Cell Interference (ICI) in a multi-cellularenvironment.

A different CSI-RS (resource) configuration is used according to thenumber of antenna ports and adjacent cells transmit CSI-RSs according todifferent (resource) configurations, if possible. Unlike CRS, CSI-RSsupports up to eight antenna ports and a total of eight antenna portsfrom antenna port 15 to antenna port 22 are allocated to CSI-RS in the3GPP standard. [Table 1] and [Table 2] list CSI-RS configurationsdefined in the 3GPP standard. Specifically, [Table 1] lists CSI-RSconfigurations in the case of a normal CP and [Table 2] lists CSI-RSconfigurations in the case of an extended CP.

TABLE 1 CSI Number of CSI reference signals configured reference 1 or 24 8 signal n_(s) n_(s) n_(s) Config- (k′, mod (k′, mod (k′, mod urationl′) 2 l′) 2 l′) 2 Frame 0 (9, 5) 0 (9, 5) 0 (9, 5) 0 structure 1 (11,2)  1 (11, 2)  1 (11, 2)  1 type 1 2 (9, 2) 1 (9, 2) 1 (9, 2) 1 and 2 3(7, 2) 1 (7, 2) 1 (7, 2) 1 4 (9, 5) 1 (9, 5) 1 (9, 5) 1 5 (8, 5) 0 (8,5) 0 6 (10, 2)  1 (10, 2)  1 7 (8, 2) 1 (8, 2) 1 8 (6, 2) 1 (6, 2) 1 9(8, 5) 1 (8, 5) 1 10 (3, 5) 0 11 (2, 5) 0 12 (5, 2) 1 13 (4, 2) 1 14 (3,2) 1 15 (2, 2) 1 16 (1, 2) 1 17 (0, 2) 1 18 (3, 5) 1 19 (2, 5) 1 Frame20 (11, 1)  1 (11, 1)  1 (11, 1)  1 structure 21 (9, 1) 1 (9, 1) 1(9, 1) 1 type 2 22 (7, 1) 1 (7, 1) 1 (7, 1) 1 only 23 (10, 1)  1 (10,1)  1 24 (8, 1) 1 (8, 1) 1 25 (6, 1) 1 (6, 1) 1 26 (5, 1) 1 27 (4, 1) 128 (3, 1) 1 29 (2, 1) 1 30 (1, 1) 1 31 (0, 1) 1

TABLE 2 CSI Number of CSI reference signals configured reference 1 or 24 8 signal n_(s) n_(s) n_(s) config- (k′, mod (k′, mod (k′, mod urationl′) 2 l′) 2 l′) 2 Frame 0 (11, 4)  0 (11, 4)  0 (11, 4) 0 structure 1(9, 4) 0 (9, 4) 0  (9, 4) 0 type 1 2 (10, 4)  1 (10, 4)  1 (10, 4) 1 and2 3 (9, 4) 1 (9, 4) 1  (9, 4) 1 4 (5, 4) 0 (5, 4) 0 5 (3, 4) 0 (3, 4) 06 (4, 4) 1 (4, 4) 1 7 (3, 4) 1 (3, 4) 1 8 (8, 4) 0 9 (6, 4) 0 10 (2, 4)0 11 (0, 4) 0 12 (7, 4) 1 13 (6, 4) 1 14 (1, 4) 1 15 (0, 4) 1 Frame 16(11, 1)  1 (11, 1)  1 (11, 1) 1 structure 17 (10, 1)  1 (10, 1)  1(10, 1) 1 type 2 18 (9, 1) 1 (9, 1) 1  (9, 1) 1 only 19 (5, 1) 1 (5, 1)1 20 (4, 1) 1 (4, 1) 1 21 (3, 1) 1 (3, 1) 1 22 (8, 1) 1 23 (7, 1) 1 24(6, 1) 1 25 (2, 1) 1 26 (1, 1) 1 27 (0, 1) 1

In [Table 1] and [Table 2], (k′,l′) represents an RE index where k′ is asubcarrier index and r is an OFDM symbol index. FIG. 11 illustratesCSI-RS configuration #0 of DL CSI-RS configurations defined in thecurrent 3GPP standard.

In addition, CSI-RS subframe configurations may be defined, each by aperiodicity in subframes, T_(CSI-RS) and a subframe offset Δ^(CSI-RS).[Table 3] lists CSI-RS subframe configurations defined in the 3GPPstandard.

TABLE 3 CSI-RS- CSI-RS periodicity CSI-RS subframe offset SubframeConfigT_(CSI-RS) Δ_(CSI-RS) I_(CSI-RS) (subframes) (subframes) 0-4 5I_(CSI-RS)  5-14 10 I_(CSI-RS) − 5  15-34 20 I_(CSI-RS) − 15 35-74 40I_(CSI-RS) − 35  75-154 80 I_(CSI-RS) − 75

Information about a Zero Power (ZP) CSI-RS is transmitted in aCSI-RS-Config-r10 message configured as illustrated in [Table 4] by RRClayer signaling. Particularly, a ZP CSI-RS resource configurationincludes zeroTxPowerSubframeConfig-r10 and a 16-bit bitmap,zeroTxPowerResourceConfigList-r10. zeroTxPowerSubframeConfig-r10indicates the CS-RS transmission periodicity and subframe offset of a ZPCSI-RS by I_(CSI-RS) illustrated in [Table 3].zeroTxPowerResourceConfigList-r10 indicates a ZP CSI-RS configuration.The elements of this bitmap indicate the respective configurationswritten in the columns for four CSI-RS antenna ports in [Table 1] or[Table 2]. That is, the current 3GPP standard defines a ZP CSI-RS onlyfor four CSI-RS antenna ports.

TABLE 4 -- ASN1START CSI-RS-Config-r10 ::= SEQUENCE {  csi-RS-r10 CHOICE{ ...  }  zeroTxPowerCSI-RS-r10 CHOICE { release NULL, setup SEQUENCE { zeroTxPowerResourceConfigList-r10 BIT STRING (SIZE (16)), zeroTxPowerSubframeConfig-r10 INTEGER (0..154) }  } } -- ASN1STOP

The current 3GPP standard defines modulation orders and cording ratesfor respective CQI indexes as illustrated in [Table 5].

TABLE 5 CQI index modulation code rate × 1024 efficiency 0 out of range1 QPSK 78 0.1523 2 QPSK 120 0.2344 3 QPSK 193 0.3770 4 QPSK 308 0.6016 5QPSK 449 0.8770 6 QPSK 602 1.1758 7 16QAM 378 1.4766 8 16QAM 490 1.91419 16QAM 616 2.4063 10 64QAM 466 2.7305 11 64QAM 567 3.3223 12 64QAM 6663.9023 13 64QAM 772 4.5234 14 64QAM 873 5.1152 15 64QAM 948 5.5547

A CQI is calculated based on interference measurement as follows.

A UE needs to measure a Signal to Interference and Noise Ratio (SINR)for CQI calculation. In this case, the UE may measure the receptionpower (S-measure) of a desired signal in an RS such as a Non-Zero Power(NZP) CSI-RS. For interference power measurement (I-measure orInterference Measurement (IM)), the UE measures the power of aninterference signal resulting from eliminating the desired signal from areceived signal.

CSI measurement subframe sets C_(CSI,0) and C_(CSI,1) may be configuredby higher-layer signaling and the subframes of each subframe set aredifferent from the subframes of the other subframe set. In this case,the UE may perform S-measure in an RS such as a CSI-RS without anyspecific subframe constraint. However, the UE should calculate CQIsseparately for the CSI measurement subframe sets C_(CSI,0) and C_(CSI,1)through separate I-measures in the CSI measurement subframe setsC_(CSI,0) and C_(CSI,1).

Hereinbelow, transmission modes for a DL data channel will be described.

A current 3GPP LTE standard specification, 3GPP TS 36.213 defines DLdata channel transmission modes as illustrated in [Table 6] and [Table7]. A DL data channel transmission mode is indicated to a UE byhigher-layer signaling, that is, RRC signaling.

TABLE 6 Transmission Transmission scheme of PDSCH mode DCI formatcorresponding to PDCCH Mode 1 DCI format 1A Single-antenna port, port 0DCI format 1 Single-antenna port, port 0 Mode 2 DCI format 1A Transmitdiversity DCI format 1 Transmit diversity Mode 3 DCI format 1A Transmitdiversity DGI format 2A Large delay CDD or Transmit diversity Mode 4 DCIformat 1A Transmit diversity DCI format 2 Closed-loop spatialmultiplexing or Transmit diversity Mode 5 DCI format 1A Transmitdiversity DCI format 1D Multi-user MIMO Mode 6 DCI format 1A Transmitdiversity DCI format 1B Closed-loop spatial multiplexing using a singletransmission layer Mode 7 DCI format 1A If the number of PBCH antennaports is one, Single-antenna port, port 0 is used, otherwise Transmitdiversity DCI format 1 Single-antenna port, port 5 Mode 8 DCI format 1AIf the number of PBCH antenna ports is one, Single-antenna port, port 0is used, otherwise Transmit diversity DCI format 2B Dual layertransmission, port 7 and 8 or single-antenna port, port 7 or 8 Mode 9DCI format 1A Non-MBSFN subframe: If the number of PBCH antenna ports isone, Single- antenna port, port 0 is used, otherwise Transmit diversityMBSFN subframe: Single-antenna port, port 7 DCI format 2C Up to 8 layertransmission, ports 7-14 or single-antenna port, port 7 or 8 Mode 10 DCIformat 1A Non-MBSFN subframe: If the number of PBCH antenna ports isone, Single- antenna port, port 0 is used, otherwise Transmit diversityMBSFN subframe: Single-antenna port, port 7 DCI format 2D Up to 8 layertransmission, ports 7-14 or single-antenna port, port 7 or 8

TABLE 7 Transmission Transmission scheme of PDSCH mode DCI formatcorresponding to PDCCH Mode 1 DCI format 1A Single-antenna port, port 0DCI format 1 Single-antenna port, port 0 Mode 2 DCI format 1A Transmitdiversity DCI format 1 Transmit diversity Mode 3 DCI format 1A Transmitdiversity DCI format 2A Transmit diversity Mode 4 DCI format 1A Transmitdiversity DCI format 2 Transmit diversity Mode 5 DCI format 1A Transmitdiversity Mode 6 DCI format 1A Transmit diversity Mode 7 DCI format 1ASingle-antenna port, port 5 DCI format 1 Single-antenna port, port 5Mode 8 DCI format 1A Single-antenna port, port 7 DCI format 2BSingle-antenna port, port 7 or 8 Mode 9 DCI format 1A Single-antennaport, port 7 DCI format 2C Single-antenna port, port 7 or 8, Mode 10 DCIformat 1A Single-antenna port, port 7 DCI format 2D Single-antenna port,port 7 or 8,

Referring to [Table 6] and [Table 7], the 3GPP LTE standardspecification defines DCI formats according to the types of RNTIs bywhich a PDCCH is masked. Particularly for C-RNTI and SPS C-RNTI, the3GPP LTE standard specification defines transmission modes and DCIformats corresponding to the transmission modes, that is, transmissionmode-based DCI formats as illustrated in [Table 6] and [Table 7]. DCIformat 1A is additionally defined for application irrespective oftransmission modes, that is, for a fall-back mode. [Table 6] illustratestransmission modes for a case where a PDCCH is masked by a C-RNTI and[Table 7] illustrates transmission modes for a case where a PDCCH ismasked by an SPS C-RNTI.

Referring to [Table 6], if a UE detects DCI format 1B by blind-decodinga PDCCH masked by a C-RNTI, the UE decodes a PDSCH, assuming that thePDSCH has been transmitted in a single layer by closed-loop spatialmultiplexing.

In [Table 6] and [Table 7], Mode 10 is a DL data channel transmissionmode for CoMP. For example, in [Table 6], if the UE detects DCI format2D by blind-decoding a PDCCH masked by a C-RNTI, the UE decodes a PDSCH,assuming that the PDSCH has been transmitted through antenna port 7 toantenna port 14, that is, based on DM-RSs by a multi-layer transmissionscheme, or assuming that the PDSCH has been transmitted through a singleantenna port, DM-RS antenna port 7 or 8.

Now a description will be given of Quasi Co-Location (QCL).

If one antenna port is quasi co-located with another antenna port, thismeans that a UE may assume that the large-scale properties of a signalreceived from one of the antenna ports (or a radio channel correspondingto the antenna port) are wholly or partially identical to those of asignal received from the other antenna port (or a radio channelcorresponding to the antenna port). The large-scale properties mayinclude Doppler spread, Doppler shift, timing offset-related averagedelay, delay spread, average gain, etc.

According to the definition of QCL, the UE may not assume that antennaports that are not quasi co-located with each other have the samelarge-scaled properties. Therefore, the UE should perform a trackingprocedure independently for the respective antenna ports in order to thefrequency offsets and timing offsets of the antenna ports.

On the other hand, the UE may performing the following operationsregarding quasi co-located antenna ports.

1) The UE may apply the estimates of a radio channel corresponding to aspecific antenna port in power-delay profile, delay spread, Dopplerspectrum, and Doppler spread to Wiener filter parameters used in channelestimation of a radio channel corresponding another antenna port quasico-located with the specific antenna port.

2) The UE may acquire time synchronization and frequency synchronizationof the specific antenna port to the quasi co-located antenna port.

3) Finally, the UE may calculate the average of Reference SignalReceived Power (RSRP) measurements of the quasi co-located antenna portsto be an average gain.

For example, it is assumed that upon receipt of DM-RS-based DL datachannel scheduling information, for example, DCI format 2C on a PDCCH(or an Enhanced PDCCH (E-PDCCH)), the UE performs channel estimation ona PDSCH using a DM-RS sequence indicated by the scheduling informationand then demodulates data.

In this case, if an antenna port configured for a DM-RS used in DL datachannel estimation is quasi co-located with an antenna port for anantenna port configured for a CRS of a serving cell, the UE may useestimated large-scale properties of a radio channel corresponding to theCRS antenna port in channel estimation of a radio channel correspondingto the DM-RS antenna port, thereby increasing the reception performanceof the DM-RS-based DL data channel.

Likewise, if the DM-RS antenna port for DL data channel estimation isquasi co-located with the CSI-RS antenna port of the serving cell, theUE may use estimated large-scale properties of the radio channelcorresponding to the CSI-RS antenna port in channel estimation of theradio channel corresponding to the DM-RS antenna port, therebyincreasing the reception performance of the DM-RS-based DL data channel.

In LTE, it is regulated that when a DL signal is transmitted in Mode 10being a CoMP transmission mode, an eNB configures one of QCL type A andQCL type B for a UE.

QCL type A is based on the premise that a CRS antenna port, a DM-RSantenna port, and a CSI-RS antenna port are quasi co-located withrespect to large-scale properties except average gain. This means thatthe same node transmits a physical channel and signals. On the otherhand, QCL type B is defined such that up to four QCL modes areconfigured for each UE by a higher-layer message to enable CoMPtransmission such as DPS or JT and a QCL mode to be used for DL signaltransmission is indicated to the UE dynamically by DCI.

DPS transmission in the case of QCL type B will be described in greaterdetail.

If node #1 having N1 antenna ports transmits CSI-RS resource #1 and node#2 having N2 antenna ports transmits CSI-RS resource #2, CSI-RS resource#1 is included in QCL mode parameter set #1 and CSI-RS resource #2 isincluded in QCL mode parameter set #2. Further, an eNB configures QCLmode parameter set #1 and CSI-RS resource #2 for a UE located within thecommon overage of node #1 and node #2 by a higher-layer signal.

Then, the eNB may perform DPS by configuring QCL mode parameter set #1for the UE when transmitting data (i.e. a PDSCH) to the UE through node#1 and QCL mode parameter set #2 for the UE when transmitting data tothe UE through node #2 by DCI. If QCL mode parameter set #1 isconfigured for the UE, the UE may assume that CSI-RS resource #1 isquasi co-located with a DM-RS and if QCL mode parameter set #2 isconfigured for the UE, the UE may assume that CSI-RS resource #2 isquasi co-located with the DM-RS.

An Active Antenna System (AAS) and Three-Dimensional (3D) beamformingwill be described below.

In a legacy cellular system, an eNB reduces ICI and increases thethroughput of UEs within a cell, for example, SINRs at the UEs bymechanical tilting or electrical tilting, which will be described belowin greater detail.

FIG. 12 illustrates antenna tilting schemes. Specifically, FIG. 12( a)illustrates an antenna configuration to which antenna tilting is notapplied, FIG. 12( b) illustrates an antenna configuration to whichmechanical tilting is applied, and FIG. 12( c) illustrates an antennaconfiguration to which both mechanical tilting and electrical titlingare applied.

A comparison between FIGS. 12( a) and 12(b) reveals that mechanicaltilting suffers from a fixed beam direction at initial antennainstallation as illustrated in FIG. 12( b). On the other hand,electrical tilting allows only a very restrictive vertical beamformingdue to cell-fixed tilting, despite the advantage of a tilting anglechangeable through an internal phase shifter as illustrated in FIG. 12(c).

FIG. 13 is a view comparing an antenna system of the related art with anAAS. Specifically, FIG. 13( a) illustrates the antenna system of therelated art and FIG. 13( b) illustrates the AAS.

Referring to FIG. 13, as compared to the antenna system of the relatedart, each of a plurality of antenna modules includes a Radio Frequency(RF) module such as a Power Amplifier (PA), that is, an active device inthe AAS. Thus, the AAS may control the power and phase on an antennamodule basis.

In general, a linear array antenna (i.e. a one-dimensional arrayantenna) such as a ULA is considered as a MIMO antenna structure. A beamthat may be formed by the one-dimensional array antenna exists on aTwo-Dimensional (2D) plane. The same thing applies to a Passive AntennaSystem (PAS)-based MIMO structure. Although a PAS-based eNB has verticalantennas and horizontal antennas, the vertical antennas may not form abeam in a vertical direction and may allow only the afore-describedmechanical tilting because the vertical antennas are in one RF module.

However, as the antenna structure of an eNB has evolved to an AAS, RFmodules are configured independently even for vertical antennas.Consequently, vertical beamforming as well as horizontal beamforming ispossible. This is called elevation beamforming.

The elevation beamforming may also be referred to as 3D beamforming inthat available beams may be formed in a 3D space along the vertical andhorizontal directions. That is, the evolution of a one-dimensional arrayantenna structure to a 2D array antenna structure enables 3Dbeamforming. 3D beamforming is not possible only when an antenna arrayis planar. Rather, 3D beamforming is possible even in a ring-shaped 3Darray structure. A feature of 3D beamforming lies in that a MIMO processtakes place in a 3D space in view of various antenna layouts other thanexisting one-dimensional antenna structures.

FIG. 14 illustrates an exemplary UE-specific beamforming in an AAS.Referring to FIG. 14, even though a UE moves forward or backward from aneNB as well as to the left and right of the eNB, a beam may be formedtoward the UE by 3D beamforming. Therefore, higher freedom is given toUE-specific beamforming.

Further, an outdoor to outdoor environment where an outdoor eNBtransmits a signal to an outdoor UE, an Outdoor to Indoor (O2I)environment where an outdoor eNB transmits a signal to an indoor UE, andan indoor to indoor environment (an indoor hotspot) where an indoor eNBtransmits a signal to an indoor UE may be considered as transmissionenvironments using an AAS-based 2D array antenna structure.

FIG. 15 illustrates an AAS-based 2D beam transmission scenario.

Referring to FIG. 15, an eNB needs to consider vertical beam steeringbased on various UE heights in relation to building heights as well asUE-specific horizontal beam steering in a real cell environment wherethere are multiple buildings in a cell. Considering this cellenvironment, very different channel characteristics from those of anexisting wireless channel environment, for example, shadowing/path losschanges according to different heights, varying fading characteristics,etc. need to be reflected.

In other words, 3D beamforming is an evolution of horizontal-onlybeamforming based on an existing linear one-dimensional array antennastructure. 3D beamforming refers to a MIMO processing scheme performedby extending to or combining with elevation beamforming or verticalbeamforming using a multi-dimensional array antenna structure such as aplanar array.

While the legacy LTE system was designed to support up to eight antennasarranged in a row, it is expected that more than eight antennas shouldbe supported due to use of a 2D antenna array in the future. Forexample, a planar array with four by four antennas along horizontal andvertical directions has 16 (4×4) physical antennas. Although eight orfewer virtual antenna ports may be defined by grouping these physicalantennas, the Degree of Freedom (DoF) in the spatial domain, brought byan increase in the number of antennas may not be fully utilized.Eventually the maximum number of antenna ports should be increased to 9or larger in order to achieve maximum performance with a maxim DoF.

If the number of antenna ports is increased to 9 or larger, CSImeasurement needs to be first considered. CRS and CSI-RS are RSs usedfor CSI measurement in the LTE system. The CRS supports only up to 4Txtransmission due to overhead. Accordingly, the CSI-RS with a smalloverhead is highly likely to be used continuously. Support of CSI-RStransmission through 9 or more antenna ports may be considered in twomethods.

New CSI-RS resources for 9 or more as antenna ports (N=9 or larger) aredefined. That is, as 4Tx CSI-RS resources are defined by extending 2TxCSI-RS resources and 8Tx CSI-RS resources are defined by extending 4TxCSI-RS resources according to the related art, 16Tx CSI-RS resources andfurther 35Tx CSI-RS resources are defined. Since new CSI-RS antennaports with indexes other than the existing antenna port indexes 15 to 22are defined, it is expected that the maximum number of antenna portswill be increased and definition of the new CSI-RS resources anddefinition of a signaling scheme for the new CSI-RS resources willaffect the conventional standards significantly.

In this context, the present invention proposes that CSI-RS transmissionthrough 9 or more antenna ports is supported using M (>1) Nm(≦8)-TxCSI-RS resources. That is, CSI-RSs are transmitted through 8 or moreantennas by configuring a plurality of CSI-RS resources within theconventional up to 8-Tx CSI-RS resources, for a single UE.

For example, if a specific node transmits CSI-RSs through 16 antennaports, the CSI-RSs are transmitted through the CSI-RS antenna portsusing two different 8-Tx CSI-RS resources. Specifically, given physicalantennas 0 to 15, antennas 0 to 7 are mapped to antenna ports #0 to #7of CSI-RS resource #1, whereas antennas 8 to 15 are mapped to antennaports #0 to #7 of CSI-RS resource #2. Resource collision may beprevented by allocating different CSI-RS configuration numbersillustrated in [Table 1] and [Table 2] and/or different CSI-RS subframeoffsets illustrated in [Table 3] between the CSI-RS resources.

Since there is no need for defining a CSI-RS for a new antenna port anda function of configuring a plurality of Non-Zero Power (NZP) CSI-RSresources for a UE is already provided, the present invention manyminimize an influence on the conventional standards.

If multiple CSI-RS resources are allocated to a single UE according tothe present invention, the afore-described QCL definition needs to beclarified more clearly.

FIG. 16 illustrates an exemplary allocation of multiple CSI-RS resourcesto a single UE according to an embodiment of the present invention.

Referring to FIG. 16, it is noted that the same node, Point A transmitsCSI-RS pattern #0 (or CSI-RS resource #0) and CSI-RS pattern #1 (orCSI-RS resource #1) and another node, Point B transmits CSI-RS pattern#2 (or CSI-RS resource #2), among three CSI-RS resources configured fora UE. If the UE receives a DL signal from Point B, a CSI-RS antenna portcorresponding to CSI-RS resource #2 is quasi co-located with a DM-RSantenna port and thus the conventional QCL definition is stilleffective.

On the other hand, if the UE receives a DL signal from Point A, the UEcannot assume QCL between CSI-RS antenna ports corresponding to CSI-RSresource port #0 and CSI-RS resource port #1 and a DM-RS resource in thecurrent LTE standard because the current LTE standard defines just QCLbetween a CSI-RS and a DM-RS or QCL between a CSI-RS and a CRS, thusallowing implicit determination of QCL between a DM-RS and a CRS,without defining QCL between a plurality of CSI-RSs.

Accordingly, the present invention configures a plurality of CSI-RSresources (or patterns) to support CSI-RS transmission through more than8 antenna ports and provides a new QCL method based on the configuredCSI-RS resources. First, based on the idea that antenna ports of aPlurality of CSI-RS resources transmitted from the same node or pointare always quasi co-located physically as illustrated in FIG. 16, thepresent invention provides a method for indicating to a UE whetherCSI-RS resources are quasi co-located with each other, when theconfiguring CSI-RS resources for a UE.

Embodiment 1

When configuring each CSI-RS resource for a UE, an eNB may indicate tothe UE whether CSI-RS antenna ports of the CSI-RS resource satisfy a QCLcondition with respect to CSI-RS antenna ports of another CSI-RSresource.

Thus, if the CSI-RS antenna ports of a specific CSI-RS resource andDM-RS antenna ports satisfy a QCL condition, the UE may assume that theCSI-RS antenna ports of another CSI-RS resource quasi co-located withthe specific CSI-RS resource are also quasi co-located with the DM-RSantenna ports.

For example, in FIG. 16, the eNB indicates to the UE that 8 CSI-RSantenna ports of CSI-RS resource #0 are quasi co-located with 8 CSI-RSantenna ports of CSI-RS resource #1. In addition, the eNB may indicateto the UE that CSI-RS resource #2 is not quasi co-located with CSI-RSresource #0 and CSI-RS resource #1.

Specifically, an Information Element (IE) or field that defines a QCLindex in relation to CSI-RS configuration may be added. That is, if theQCL indexes of two CSI-RS resources are identical, the CSI-RS antennaports of the two CSI-RS resources are quasi co-located. If the QCLindexes of the two CSI-RS resources are different, the CSI-RS antennaports of the two CSI-RS resources are not quasi co-located.

In other words, if the QCL indexes of the two CSI-RS resources areidentical as is the case between CSI-RS resource #0 and CSI-RS resource#1 in FIG. 16, this implies that the CSI-RS antenna ports of the twoCSI-RS resources are transmitted from the same node. On the contrary, ifthe QCL indexes of the two CSI-RS resources are different, this impliesthat the CSI-RS antenna ports of the two CSI-RS resources aretransmitted from different nodes.

[Table 8] and [Table 9] illustrate examples of adding an IE that definesa QCL index in relation to CSI-RS configuration to a 3GPP standardspecification, TS 36.331 according to the embodiment of the presentinvention.

TABLE 8 -- ASN1START CSI-RS-ConfigNZP-r11 ::= SEQUENCE {csi-RS-IdentityNZP-r11 CSI-RS-IdentityNZP-r11, antennaPortsCount-r11ENUMERATED (an1, an2, an4, an8}, resourceConfig-r11 INTEGER (0..31),subframeConfig-r11 INTEGER (0..154), scramblingIdentity-r11 INTEGER(0..503), qcl-identity qcl-identity qcl-CRS-Info-r11 SEQUENCE {qcl-ScramblingIdentity-r11 INTEGER (0..503}, crs-PortsCount-r11ENUMERATED {n1, n2, n4, spare1}, mbsfn-SubframeConfig-r11MBSFN-SubframeConfig OPTIONAL -- Need OR } OPTIONAL, -- Need OR ... } --ASN1STOP

TABLE 9 -- ASN1START qcl-identity ::= INTEGER (1..maxQCL-identity) --ASN1STOP

Referring to [Table 9], a QCL index may be set in a “qcl-identity”field, which may be an integer ranging from 1 to a maximum value,maxQCL-identity. The value of maxQCL-identity may be preset by a systemor signaled by the eNB.

The QCL index may be included in CSI-RS-ConfigNZP IE orCSI-RS-IdentityNZP IE of an RRC message, indicating whether each NZPCSI-RS resources is quasi co-located, as illustrated in [Table 8]. Orthe QCL index may be included in CSI-process IE or CSI-ProcessIdentityIE, indicating whether the CSI-RS antenna ports of each CSI process arequasi co-located.

Furthermore, a method for explicitly indicating a quasi co-locatedCSI-RS resource, a quasi co-located reference CSI-RS resource, or a baseco-located reference CSI-RS resource may be considered. For example,when CSI-RS resource #1 is configured in FIG. 16, it may be explicitlyindicated that CSI-RS resource #1 is quasi co-located with CSI-RSresource #0. This method may still use the CSI-RS-IdentityNZP IE orCSI-ProcessIdentity IE of the current RRC message.

That is, the index of an NZP CSI-RS resource or CSI process quasico-located with a corresponding CSI-RS resource may be indicated.Specifically, the index of an NZP CSI-RS RS resources quasi co-locatedwith a corresponding NZP CSI-RS resources may be added asCSI-RS-IdentityNZP in the CSI-RS-ConfigNZP IE, as illustrated in [Table10]. In the absence of a quasi co-located CSI-RS resource or if thecorresponding CSI-RS resource is a reference (or base) CSI-RS resource,the field may be omitted.

TABLE 10 -- ASN1START CSI-RS-ConfigNZP-r11 ::= SEQUENCE {csi-RS-IdentityNZP-r11 CSI-RS-IdentityNZP-r11, antennaPortsCount-r11ENUMERATED {an1, an2, an4, an8}, resourceConfig-r11 INTEGER (0..31),subframeConfig-r11 INTEGER (0..154), scramblingIdentity-r11 INTEGER(0..503), qcl-CSI-RS-IdentityNZP  CSI-RS-IdentityNZP-r11qcl-CRS-Info-r11 SEQUENCE { qcl-ScramblingIdentity-r11 INTEGER (0..503),crs-PortsCount-r11 ENUMERATED {n1, n2, n4, spare1},mbsfn-SubframeConfig-r11 MBSFN-SubframeConfig OPTIONAL -- Need OR }OPTIONAL, -- Need OR ... } -- ASN1STOP

Embodiment 2

In the foregoing embodiment of the present invention, CSI-RStransmission through 9 or more CSI-RS antenna ports is supported byindicating the QCL relationship between CSI-RS resources. Compared tothe forgoing embodiment of the present invention, this embodiment of thepresent invention proposes that a QCL type or QCL parameter set is addedan existing QCL type or QCL parameter set is modified in order toreflect QCL between DM-RS antenna ports and CSI-RS antenna portscorresponding to a plurality of NZP CSI-RS resources.

In this embodiment of the present invention, QCL type A may be modifiedsuch that DM-RS antenna ports may be quasi co-located with CRS antennaports and CSI-RS antenna ports corresponding to a plurality of CSI-RSresources. In the case of QCL type B, when a plurality of QCL parametersets are defined by a higher-layer message, a QCL parameter set withDM-RS antenna ports quasi co-located with CSI-RS antenna portscorresponding to a plurality of CSI-RS resources may be newly defined,extended, or modified.

For example, a method for setting a plurality of CSI-RS resource-relatedIEs for QCL configuration by a high-layer message may be considered.[Table 11] illustrates IEs of a QCL configuration parameter set in acurrent LTE standard specification and [Table 12] illustrates a modifiedQCL configuration parameter set according to the embodiment of thepresent invention.

TABLE 11 PDSCH-RE-MappingQCL-Config-r11 ::= SEQUENCE {pdsch-RE-MappingQCL-ConfigId-r11 PDSCH-RE-MappingQCL-ConfigId-r11,optionalSetOfFields-r11 SEQUENCE { crs-PortsCount-r11 ENUMERATED {n1,n2, n4 , spare1}, crs-FreqShift-r11 INTEGER (0..5),mbsfn-SubframeConfig-r11 MBSFN-SubframeConfig OPTIONAL, -- Need ORpdsch-Start-r11 ENUMERATED {reserved, n1, n2, n3, n4, assigned} }OPTIONAL, -- Need OP csi-RS-IdentityZP-r11 CSI-RS-IdentityZP-r11,qcl-CSI-RS-IdentityNZP-r11 CSI-RS-IdentityNZP-r11 OPTIONAL, -- Need OR... }

TABLE 12 PDSCH-RE-MappingQCL-Config-r11 ::= SEQUENCE {pdsch-RE-MappingQCL-ConfigId-r11 PDSCH-RE-MappingQCL-ConfigId-r11,optionalSetOfFields-r11 SEQUENCE { crs-PortsCount-r11 ENUMERATED {n1,n2, n4, spare1}, crs-FreqShift-r11 INTEGER (0..5),mbsfn-SubframeConfig-r11 MBSFN-SubframeConfig OPTIONAL, -- Need ORpdsch-Start-r11 ENUMERATED {reserved, n1, n2, n3, n4, assigned} }OPTIONAL, -- Need OP csi-RS-IdentityZP-r11 CSI-RS-IdentityZP-r11,qcl-CSI-RS-IdentityNZP-r11 SEQUENCE OF CSI-RS-IdentityNZP-r11OPTIONAL, -- Need OR ... }

Compared to [Table 11], it is noted from [Table 12] that“CSI-RS-IdentityNZP-r11” indicating one CSI-RS resource is replaced with“SEQUENCE OF CSI-RS-IdentityNZP-r11” indicating a plurality of CSI-RSresources, for QCL assumption.

FIG. 17 is a block diagram of a communication apparatus according to anembodiment of the present invention.

Referring to FIG. 17, a communication apparatus 1700 includes aprocessor 1710, a memory 1720, an RF module 1730, a display module 1740,and a User Interface (UI) module 1750.

The communication device 1700 is shown as having the configurationillustrated in FIG. 17, for the convenience of description. Some modulesmay be added to or omitted from the communication apparatus 1700. Inaddition, a module of the communication apparatus 1700 may be dividedinto more modules. The processor 1710 is configured to performoperations according to the embodiments of the present inventiondescribed before with reference to the drawings. Specifically, fordetailed operations of the processor 1710, the descriptions of FIGS. 1to 16 may be referred to.

The memory 1720 is connected to the processor 1710 and stores anOperating System (OS), applications, program codes, data, etc. The RFmodule 1730, which is connected to the processor 1710, upconverts abaseband signal to an RF signal or downconverts an RF signal to abaseband signal. For this purpose, the RF module 1730 performsdigital-to-analog conversion, amplification, filtering, and frequencyupconversion or performs these processes reversely. The display module1740 is connected to the processor 1710 and displays various types ofinformation. The display module 1740 may be configured as, not limitedto, a known component such as a Liquid Crystal Display (LCD), a LightEmitting Diode (LED) display, and an Organic Light Emitting Diode (OLED)display. The UI module 1750 is connected to the processor 1710 and maybe configured with a combination of known user interfaces such as akeypad, a touch screen, etc.

The embodiments of the present invention described above arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim by asubsequent amendment after the application is filed.

A specific operation described as performed by a BS may be performed byan upper node of the BS. Namely, it is apparent that, in a networkcomprised of a plurality of network nodes including a BS, variousoperations performed for communication with a UE may be performed by theBS, or network nodes other than the BS. The term ‘BS’ may be replacedwith the term ‘fixed station’, ‘Node B’, ‘evolved Node B (eNode B oreNB)’, ‘Access Point (AP)’, etc.

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof. In a hardware configuration, the methods according to exemplaryembodiments of the present invention may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, an embodiment of the presentinvention may be implemented in the form of a module, a procedure, afunction, etc. Software code may be stored in a memory unit and executedby a processor. The memory unit is located at the interior or exteriorof the processor and may transmit and receive data to and from theprocessor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

The method and apparatus for configuring QCL between antenna ports formassive MIMO in a wireless communication system have been described inthe context of a 3GPP LTE system. Besides, the present invention isapplicable to many other wireless communication systems.

1. A method for receiving a Reference Signal (RS) at a User Equipment(UE) in a wireless communication system, the method comprising:receiving information about a plurality of RSs through a high layer; andreceiving the RS based on the information about the plurality of RSsfrom at least one node, wherein the information about the plurality ofRSs includes information indicating whether it is possible to assumequasi co-location between at least two RSs of the plurality of RSs. 2.The method according to claim 1, wherein if it is possible to assumequasi co-location between at least two RSs of the plurality of RSs, itis assumed that the at least two RSs have a same large-scale property.3. The method according to claim 2, wherein the large-scale propertyincludes at least one of Doppler spread, Doppler shift, average delay,and delay spread.
 4. The method according to claim 1, wherein the RS isa Channel State Information Reference Signal (CSI-RS).
 5. The methodaccording to claim 1, wherein: one of the at least two RSs is a defaultRS, and the information indicating whether it is possible to assumequasi co-location between the at least two RSs of the plurality of RSsincludes information indicating whether it is possible to assume thatanother RS of the at least two RSs is quasi co-located with the defaultRS.
 6. The method according to claim 1, wherein: the information aboutthe plurality of RSs includes resource configuration information abouteach of the plurality of RSs, the resource configuration informationhaving a specific field for quasi co-location assumption, and if thespecific fields of the resource configuration information about at leasttwo RSs are same, it is possible to assume that the at least two RSs arequasi co-located.
 7. The method according to claim 1, wherein the atleast two RSs assumed to be quasi co-located are transmitted from thesame node.
 8. A method for transmitting a Reference Signal (RS) to aUser Equipment (UE) by a network in a wireless communication system, themethod comprising: transmitting information about a plurality of RSs tothe UE through a high layer; and transmitting the RS based on theinformation about the plurality of RSs to the UE through at least onenode, wherein the information about the plurality of RSs includesinformation indicating whether it is possible to assume quasico-location between at least two RSs of the plurality of RSs.
 9. Themethod according to claim 8, wherein if it is possible to assume quasico-location between at least two RSs of the plurality of RSs, the UEassumes that the at least two RSs have a same large-scale property. 10.The method according to claim 9, wherein the large-scale propertyincludes at least one of Doppler spread, Doppler shift, average delay,and delay spread.
 11. The method according to claim 8, wherein the RS isa Channel State Information Reference Signal (CSI-RS).
 12. The methodaccording to claim 8, wherein: one of the at least two RSs is a defaultRS, and the information indicating whether it is possible to assumequasi co-location between the at least two RSs of the plurality of RSsincludes information indicating whether it is possible to assume thatanother RS of the at least two RSs is quasi co-located with the defaultRS.
 13. The method according to claim 8, wherein: the information aboutthe plurality of RSs includes resource configuration information abouteach of the plurality of RSs, the resource configuration informationhaving a specific field for quasi co-location assumption, and if thespecific fields of the resource configuration information about at leasttwo RSs are same, it is possible for the UE to assume that the at leasttwo RSs are quasi co-located.
 14. The method according to claim 8,wherein the at least two RSs assumed to be quasi co-located aretransmitted through the same node.